In recent years, as one of mechanisms for raising pressure in a pressurizing chamber formed in a substrate of an actuator, a mechanism has been known in which the volume of the pressurizing chamber is changed by displacement of a piezoelectric/electrostrictive device disposed in a pressurizing chamber wall. Moreover, such a piezoelectric/electrostrictive actuator is used, for example, as an ink pump of a print head for use in an ink jet printer. When ink is supplied and the pressure in the charged pressurizing chamber is raised by the displacement of the piezoelectric/electrostrictive device, ink particles (droplets) are ejected from nozzle holes connected to the pressurizing chamber to perform printing.
For example, in JP-A-6-40035, one example of an ink jet print head using the piezoelectric/electrostrictive actuator, as shown in the accompanying FIGS. 4 and 5 and described below, is disclosed. An ink jet print head 140 is formed by bonding/integrating an ink nozzle member 142 and piezoelectric/electrostrictive film type actuator 145, and the ink supplied to a cavity 146 formed in the piezoelectric/electrostrictive film type actuator 145 is spouted through nozzle holes 154 disposed in the ink nozzle member 142.
In more detail, the piezoelectric/electrostrictive film type actuator 145 is constituted of a ceramic substrate 144 and a piezoelectric/electrostrictive device 178 integrally formed in the ceramic substrate 144. The ceramic substrate 144 is integrally formed including a structure in which a closing plate 166 and connection plate 168, each having a thin flat plate shape, are stacked via a spacer plate 170.
In the structure, a first opening for connection 172 and second opening for connection 174 are formed in the connection plate 168 in positions opposing through hole 156 and orifice hole 158, respectively, which are formed in an orifice plate 150 of the ink nozzle member 142. It is to be noted that the first opening for connection 172 has an inner diameter substantially the same as or slightly larger than that of the through hole 156. On the other hand, the diameter of the second opening for connection 174 is set to be larger than that of the orifice hole 158 by a predetermined dimension.
Moreover, a plurality of longitudinally rectangular windows 176 are formed in the spacer plate 170. Moreover, the spacer plate 170 is stacked onto the connection plate 168 so that the first opening for connection 172 and second opening for connection 174 disposed in the connection plate 168 are opened to the respective windows 176.
Furthermore, the closing plate 166 is stacked on the surface of the spacer plate 170 on the opposite side that the connection plate 168 is stacked, and the openings of the windows 176 are covered with this closing plate 166. Accordingly, a cavity 146 connected to the outside through the first and second openings for connection 172, 174 is formed in the ceramic substrate 144.
However, in the piezoelectric/electrostrictive film type actuator 145, in order to obtain a large displacement for ejecting larger droplets, it is effective to reduce the thickness of the closing plate 166 (vibration plate) or to enlarge the width of the longitudinally rectangular window 176 (cavity 146) in the short-side direction, but there is a problem that the rigidity decreases and a high-speed response is impaired.
On the other hand, the rigidity needs to be enhanced in order to obtain more superior high-speed response, and it is effective to increase the thickness of the closing plate 166 (vibration plate) or to reduce the width of the longitudinally rectangular window 176 (cavity 146) in the short-side direction, but then there is a problem that the displacement is reduced and the necessary amount of droplets cannot be ejected. That is, in the demand for a higher capability piezoelectric/electrostrictive actuator, it has been difficult to establish both a large displacement and a high-speed response only by dimensional optimization.
The present invention has been developed considering the problems of the related art and an object thereof is to provide a superior piezoelectric/electrostrictive film type actuator which can easily be highly integrated, without including a laminated structure using an adhesive, in which a larger displacement is obtained with the same driving voltage, which has a fast response speed and a large generation force, and a method of manufacturing the actuator.